hello you ken use a power transistor with 50amp or less connect to de pic with 2 resistor one 12k to ground and the other to the gate 10k in the same line and work with the pwm 0 to 100 scale =0 to 255 the power transistor work from 0 to 30v ....
use one diode to the motor (50v)

I have this working in my Robot for long time no problem....